Air Barrier Membrane Install

It seemed that it took getting the new doors and windows installed before the time was right to finally install the membrane. I made the decision to use the vapor permeable air barrier from Siga in October of 2013. We have had the membrane and tapes for over a year. Here they were sitting quietly in the corner waiting for me to finally start the job.

Siga Majpell Membrane

The first step is hanging the double sided tape over the rafters. These work on wood or metal and about any surface–here on the polyiso layer.

Siga Twinet Tape on Ceiling

The second step is to cut the membrane to length, with enough to overlap the next piece. Since we have the top plate of the bathroom hanging wall left on this ceiling, we cut enough to cover the room lengthwise.
The application was difficult as the heavy piece of membrane was too much for the Twinet double sided tape. I ended up stapling the membrane at the top and finally got it to stick to the tape but the first piece ended up a little uneven.

First Application Uneven in Spots

The cover on the tape is pulled down as the membrane is installed. Here the first layer is done and the tape is hanging ready for the second row.

Ready for Second Row

The overlapped edges are taped with the Sicrall tape here. Siga no longer makes this paper backed tape, they replaced it with a vinyl tape. But this tape holds quite well and with its paper backing is easy to install. The caulking at the edges complete the air barrier. I’m using the Siga Primur caulk that works on stucco but I also used it at the wood edges for the first room. The caulk looks like it has some silicone in it as it dries half clear/half white, but it stays tacky a long time. It probably stays rubbery to maintain a seal even if the substrates have some movement.

Installed taped and caulked edges

We started the job trying to use just one layer of scaffolding with a ladder on top. But the ceiling was still too high and partially was the reason the first piece was so difficult to maneuver. So for the caulking job and for the kitchen membrane, I added the second set of scaffolding and it allows for much easier contact with the highest part of the cathedral ceiling.

Double Decker Scaffolding

Unfortunately when rearranging the bottom set of scaffolding, I was having a problem lowering the platform. In the past I had easily dropped it a hole or two at a time but this time it was not working. It wasn’t until I tried to lower it from the side that the platform completely dropped off and landed on my left foot that I realized the problem was the platform was NOT bolted on. So the whole scaffolding had been a bit more rickety than I remembered and that little difference made for a very sore foot. Luckily I didn’t break any toes. When I reassembled it I found the bolts and USED them. Then I had to take it apart again to move it to the kitchen to install that ceiling membrane.